This invention relates to a method of manufacturing a pultruded part which is particularly but not exclusively developed for manufacturing a spacer for a sealed window unit which is manufactured so that it is moisture impermeable.
As is well known, sealed window units comprise two glass panes which are coextensive so that the edges are overlying, a spacer element which is arranged at each edge of the panes and holds the panes in the properly spaced relationship and a sealing material which is applied around the exterior of the spacer. It is essential that moisture does not enter the area between the panes since that moisture will then condense on one of the panes and prevent the proper transparency of the window unit. For this purpose a dessicant is generally introduced into the hollow interior of the spacer and the spacer is designed either by a slot or by other techniques so that the moisture that remains within the area between the panes can escape for collection by the desicant. It is also essential that the spacer is sealed relative to the panes so that no moisture can enter from the exterior edges of the window unit.
Conventionally such spacers have been manufactured from aluminum which is entirely moisture impermeable. Aluminum spacers have a number of disadvantages however particularly in relation to the thermal expansion characteristics and the relatively high thermal conductivity.
Many attempts have been made therefore over the years to design a spacer which is manufactured from other materials. Many of these attempts have failed completely. One attempt which has met with a significant degree of success is that shown in European Patent Publication No. 113209 which shows a spacer which is manufactured by pultrusion from a thermosetting resin material which is reinforced by fibers which are preferably glass fibers. This spacer has the advantage of an improved thermal conductivity and a coefficient of thermal expansion which is much closer to that of glass.
One problem which has arisen with a product of this type is that the resin material is not itself impermeable to moisture so that it is possible for moisture to penetrate the part known as moisture vapor transmission or MVT so that the moisture can enter the area between the panes and interfere with the proper usage of the product.
One solution to this problem has been to replace the conventional sealant around the outside of the spacer by an improved sealant which itself is impermeable to moisture and thus prevents the moisture from reaching the spacer itself. However this disadvantage of the poorer MVT of the spacer has led to some adverse criticism and a reduction in the success which should otherwise be achieved in view of the improvements in other qualities relative to the conventionally used aluminum.
It is known that foil material when applied as a layer on an outer surface of a part can provide a complete impermeability to moisture. Attempts have therefore been made to adhesively attach a foil onto the exterior of a part and particularly to the exterior of a spacer formed from a resin material so as to provide for the spacer an improved MVT. However this technique is unsatisfactory in that it requires the adhesive application of a foil in an additional step, it leaves the foil exposed and accessible to damage and it weakens the structure of the part since the foil can be torn away. This technique has therefore achieved little success.